In rotary offset printing, ink is applied to an image plate mounted on one cylinder. The ink is transferred to a resilient blanket on a second cylinder. A paper web is imprinted with the ink on the blanket. The plate and blanket cylinders have to hold the plate or blanket on the cylinder surface. Cylinders have been used which hold the plate magnetically. Magnetic cylinders must have sufficient holding capability for reliable operation in rotary web offset printing.
As discussed in Peekna, U.S. Pat. No. 4,676,161, and Wouch et al., U.S. Pat. No. 4,817,527, owned by the assignee hereof, a typical blanket for a magnetic cylinder includes a carrier plate of magnetic material having a length substantially equal to half the circumference of the cylinder. An elongate blanket sheet has a length also substantially equal to half the circumference of the cylinder. The blanket sheet is secured to an outer surface of the carrier plate. Two blankets are used on each cylinder. A concern has been raised that, in use, it is possible that peel-off can occur at the leading edge of either printing blanket. Also, circumferential displacement of the printing blanket about the cylinder can occur.
The present invention is intended to overcome one or more of the problems discussed above.